Despite disabling the feature, T-Mobile shows you how to setup Wi-Fi Calling on the Google Nexus 4
still planning on disabling the feature. Right on the website are directions for setting up Wi-Fi calling including instructions for hooking up 9-1-1 to the feature, and setting your network preferences. The question is why would T-Mobile show these directions if the carrier has disabled the feature. There could be a legitimate answer.
The 8GB model of the Google Nexus 4 will be $199 from T-Mobile with a signed two-year pact. The same model from the Google Play Store will be $299 off contract. Those who desire Wi-Fi Calling because they have poor phone reception, or who want the Google Play Store version because there are no handcuffs, could pay the extra $100 for the unlocked phone, and still hook up to T-Mobile's speedy 42Mbps HSPA+ pipeline. Perhaps for these customers, T-Mobile has posted the instructions for Wi-Fi calling. Or just maybe T-Mobile has changed its mind and will support Wi-Fi calling on its branded version of the phone. We have a call into T-Mobile for clarification and will try to get an answer to you.
source: T-Mobile via AndroidAuthority
UPDATE: A T-Mobile spokesman has informed us that the support page for the Google Nexus 4 is incorrect and that it is confirmed that T-Mobile will not enable Wi-Fi calling on the Google Nexus 4